Band-filter coupling circuit for television amplifiers



' Dec. 3, 1940- K. SCHLESINGER BAND-FILTER COUPLING CIRCUIT FORTELEVISION AMPLIFIERS Filed April 12, 1957' /i shorf wave range A longwave range [/7 Men for":

Patented Dec. 3, 1940 UNITED; STATES BAND-FILTER. COUPLING CIRCUIT FURTELEVISION AMPLIFIERS 'Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc, a corporation of New YorkApplication April 12,

1937, Serial No. 136,412

In Germany April 16, 1936 2 Claims.

The present invention relates to band-filter circuits for couplingamplifier arrangements used for amplifying wide frequency-bands as theyare used for television purposes.

In intermediate-frequency amplifiers for television superheterodynes'and transmission amplifiers for television purposes coupling circuitsare known which consist of a pair of coils, each single coil being tunedper se to the unmodulated carrier wave and the two coils being sotightly coupled together that the frequency-curve of this circuit issufliciently wide to cover the television frequency band. It is knownthat band-filter coils of this nature such, for example, as alreadydescribed in the application Ser. No. 24,901 of June 4, 1935, Patent No.2,131,193, issued Sept. 27th, 1938, drop off sharply only in theshortwave range whilst in the long-wave range they strive to reach anextreme value in the quality of transformation, which is not zero. Thereis required, however, in the present television art a transformationwhich drops 01? equally towards both sides.

In the accompanying drawing embodiments of 25 band-filter circuits inaccordance with the invention are shown.

Fig. 1 shows a band-filter circuit for transmitting a wide frequencyband. The curve of the frequency range transmitted by this arrangementhas a sharply dropping off at both sides of the frequency band.

Fig. 2 shows the curve of the frequency band transmitted by the circuitshown in Fig. 1.

Fig. 3 shows a further embodiment of the band- 35 filter circuitaccording to the invention.

In Fig. 1 a first embodiment of a transformation of this character isshown, which avoids the stated disadvantage of the purely inductivesystern. The primary coil 1 is not directly con- 40 nected to the anodeof the first tube 3, butis coupled by way of a condenser 4. The tube 3itself acts in direct fashion on an ohmic resistance 5. The condenser 4and the primary inductance I are so tuned in relation to one anotherthat series resonance occurs on a wave adjustable by condenser 4, whichwave has a frequency lying in that end of the side-band frequencyspectrum which contains the higher frequencies (short wave end).

On the other hand the secondary inductance 2 with the accompanyinginherent and grid capacity 6 is tuned to a wave which has a frequencylying in the long-wave range of the spectrum or even beyond thelong-wave end. There then occurs the effect to be seen from Fig. 2.

The curve a represents the resistance amplification occurring 'at theresistance 5. As well known, this decreases after short waves inproportion to the wave-length owing to the accompanying capacities. 1

The curve b represents the potential across the primary coil I. This hasa resonance maximum at l, which is adjusted by series resonance between4 and I. The magnetic field is represented by a curve 0, and fades lessquickly than the 10 potential in the long-wave range of the frequencyspectrum. The curve d shows the potential across the secondary coilexcited by a constant field. Owing to the natural resonance this curvepossessesa resonance peak at 8, and towards the lower frequencies itdescends in proportion to the frequency.

The final curve e results from the superimposing of the coupling fieldcurve 0 and the fre-. quency curve d of the secondary circuit. Thisfinal curve descends in the short-wave range of the frequency spectrumin similar fashion to the field curve 0. In the long-wave range,however, it drops very considerably owing to the effect of the couplingcondenser 4 according to the invention. The desired result is atransformation curve which is limited sharply towards both ends.

To avoid plastic effects at the image screen both coils must be dampedat least aperiodically by means of resistances 9 and It). The resistance5 cannot be made larger than it is determined by the shunted inherentcapacities.

Practical dimensions are approximately as follows:

Television image 400 lines, 25 images per second Width of side band,twice 1.6 Resistance 5, 2.500 ohms. Condenser 4=0.2-10 -0.6-10 ,lfResistance 9, 7.500 ohms Resistance H], 5.000 ohms Coil I havingresonance effect at approximately 60 metre wavelength Coil 2 havingresonance effect at approximately 120 metre wavelength Carrier wave, 70metres Extreme side waves, 50 metres and 150 metres resistance [5.

The condenser H connected between the primary and the anode of the tube3 corresponds to condenser 4 in Fig. 1. Further an additional condenserI3 is arranged between the secondary and the grid of the succeedingtube. This condenser is thus dimensioned as to effect in combinationwith the natural frequency of the secondary a sharp cutting-off of thatend of the broad television frequency band which extends towards the lowfrequency values.

There is common to both of said circuit systems shown in Figs. 1 and 3 acombination of capacitative and inductive coupling, the capacitativecouplings producing series resonance in the short-wave range and theinductive couplings resonance in the long-wave range.

I claim: 1

1. In a television amplifier arrangemenumore particularly forintermediate-frequency amplifier systems, the use of a combinedinductive and capacitative coupling circuit between two succeeding tubeshaving atleast a cathode, a grid and a plate, comprising a, transformer,damping resistances connected in parallel to the primary and secondaryof said transformer, and a variable condenser, the primary of saidtransformer being connected to the plate of the preceding tube via saidvariablecondenser in serial connection, said variablecondenser being soadjusted as to fall in resonance with said primary at the high-frequencyend of the frequency band to be transmitted, the secondary beingconnected between grid and cathode of the associated tube and tuned withthe associated inherent capacities to the low-frequency end of thefrequency band to be transmitted.

2. In a television amplifier arrangement, more particularly forintermediate-frequency amplifier 1 systems, the use of a combinedinductive and capacitative coupling circuit between two succeeding tubeshaving at least a cathode, a grid and a plate, comprising a transformer,damping resistances connected in parallel to the primary and secondaryof said transformer, and a variable condenser, the primary of saidtransformer being connected tothe plate of the preceding tube via saidvariable condenser in serial connection, said variable condenser beingso adjusted as to fall in resonance with said primary at thehigh-frequency end of the frequency band to be transmitted, thesecondary being connected between grid and cathode of the associatedtube and tuned with the associated-inherent capacities to thelow-frequency end of the frequency band to be transmitted, a condenserbeing inserted between said secondary and the grid of said associatedtube.

- KURT SCHLESDIGER.

